1. Field of the Invention
The present invention relates to an apparatus for fixing the longitudinal position of a shaft in a bore and, more particularly, to an apparatus for mounting the valve stem of a fluid control valve in the valve body in such fashion as to maintain the valve element centered relative to the valve seat.
2. Description of the Prior Art
There are many instances when it is desirable to be able to fix the longitudinal position of a shaft in the bore of a body in such manner that axial forces will not cause relative shifting of the shaft in the bore. It is, of course, a requirement of most such mountings that the shaft continue to be free to rotate. One such instance is found in valves.
Valves employing pivotal closure elements, such as butterfly valves and the like, are widely used in industry for fluid handling control. In particular, butterfly valves employing resilient sealing means engaging rigid metal members are extensively used in a wide variety of environments since a good pressure tight seal can be obtained. This is due, at least in part, to the deflection or resiliency of the sealing means carried by either the valve disk or the valve body. However, even though a valve can initially be assembled such that the valve element, e.g. disk, is properly centered to seal, it is important that the disk remain centered or aligned with respect to the seat under the influence of axial forces acting on the stem(s) which rotatively mount the disk in the valve body. For example, actuators are frequently mounted on valves to control the disk. Often, in order to secure the actuator to the stem, a pounding force must be exerted on the actuator. The force translates into a force acting longitudinally on the valve stem which can move the disk out of its centered position with respect to the seat resulting in a tendency for the valve to leak.